Cathode structure for electric discharge tubes



Patented Oct. 25, 1949 CATHODE STRUCTURE FOR ELECTRIC vDISCHARGE TUBESJohanl Lodewijk Hendrik Jonker, Eindhoven, Netherlands, assgnor toHartford National Bank and Trust Company, Hartford, Conn.,

trustee Application July 20, 1946, Serial No. 685,157 In the NetherlandsDecember 31, 1943 Section 1, Public Law 690, August 8, 1946 Patentexpires December 31, 1963 (Cl. Z50-27.5)

2 Claims.

This invention relates toan electric discharge tube and particularly tothe cathode of such a tube.

1t is often desirable that the thickness of the emitting layer of acathode for `discharge tubes, particularly rectifier and amplier valves,should be a minimum in order to ensure a low resistance across the layerand in addition satisfactory adherence of this layer to the support. Avery thin emitting layer may, however, have the disadvantage that thequantity of the emitting substance is low so that the cathode has a Wlife.

It is known to provide cathodes with a large supply of emitting materialby housing this material in a small thin-walled tube which is heateddirect and in which the active metal is outwardly diffused through thewall of this tube; While the cathode is in use; such a cathode acts asthough it comprises a thin emitting layer, whilst at the same time alarge supply of emitting material is internally available for subsequentsupply. This subsequent supply, however, proceeds comparatively slowlyso that nevertheless fatigue phenomena may occur.

In addition, for the purpose of avoiding cathode disintegration due tobombardment by electrons with cathodes for X-ray tubes, amplifier valvesor the like, it is known to coat the emissive layer applied to theconductive substratum with a very thin metal layer. This, however, doeslnot introduce any change in the essential construction of the cathodesince the resistance across the emissive layer keeps on being importantbecause only the support of the emitting layer is provided with acurrent conductor and the emission current must traverse the layer ofthe emissive material.

According to the invention, these disadvantages can be obviated by theuse of a cathode in which a metal supporting body has applied to it anemitting layer which in turn is coated with a metal lm or a conductivecoating of different shape and in which this coating is provided with acurrent supply conductor.

This simple construction has several advantages. The emission currentbeing carried oi direct by the metal external layer, it is possible touse such a thick emitting layer as is required for the obtainment of asujiciently high life, whereas the emission proper ensues from anextremely thin layer that is formed on the outer side of this metal ilmWhile the cathode is in use.

As set out hereinbefore, the lm on the emitting material must haveconnected to it a current conductor; in this case it is 4not essentialthat such a conductor should also be connected to the conductive supportof the emitting layer but particular advantages may be secured thereby.lIf indeed the two conductive bodies are connected to separate currentconductors, the resistance across the layer and thus the subsequentsupply and the emission may be favourably inuenced if a low potentialdifference is applied between the two conductors. This potentialdiierence is for example lower than l0 volts and at any rate lower thanvolts of direct tension. This tension results in a certain electrolysisof the emissive oxides and this assists in the subsequent supply ofemissive substance to the surface of the external layer.

For the supporting body and the emissive layer use may be made of thesame materials from which an oxide cathode is generally built up; thus,for example, the support may be constituted by nickel, copper, tungsten,molybdenum or similar metals and the emissive layer by one or morealkaline earth oxides. The external layer applied to this emissive layermay also be constituted by a metal such as nickel and may be of widelydifferent form and structure. Thus for example, it may be constituted asa foil having a thickness of a few microns; according to one embodimentof the present invention, by which important advantages are secured,this layer is, however, constituted by a nickel wire gauze which isapplied to the emissive layer; a further embodiment consists for examplein a wire which is wound around the cathode in the form of a spiral orof a helix.

In order that the invention may be clearly understood and readilycarried into effect it will now be described more fully with referenceto the accompanying drawing, in which the single figure diagrammaticallyshows an electrode system of a tube according to the invention.

Referring to the iigure, I designates a heating element which by meansof insulating material may be separated from the support 2 for theemissive layer 3; this emissive layer 3 has applied to it a conductivelm 4 constituted by a nickel wire gauze folded and welded around thecathode. The cathode thus constructed is surrounded by a grid 5 and ananode 6; the electrodes are centered by means of mica discs 'I and 8.The aggregate is housed in a bulb 9 sealed by a disc I0. This disc hassealed in it the contact members II of the tube and these contactmembers are connected on the inside of the tube to the various currentsupply conductors of the electrodes, to Wit the conductor I2 for theanode, the conductor I3 `for the grid, the conductors I4 for the heatingelement and finally the conductors l5 and I6 which are connectedrespectively to the support of the emitting material and the conductivelm on the emitting material; the corresponding connecting conductors ofthe tube may have the desired potential difference applied between them.

What I claim is:

1. An electric discharge device comprising an anode and an indirectlyheated cathode, said cathode embodying a heater, a conductive supportadjacent to the heater, but electrically insulated therefrom, a layer ofa readily emitting substance on the support, a conductive coating onsaid substance, a current supply conductor connected to said conductivecoating and having a terminal for connection to an external circuit, anda separate supply conductor connected to the conductive support for thecathode and having a terminal for connection to an external circuit.

2. An electric discharge device comprising an anode and an indirectlyheated cathode, said cathode embodying a centrally located heater, acylindrical conductive support about said heater, but electricallyinsulated therefrom, a layer of a readily emitting substance on thesupport, a conductive coating of metal wire gauze about said substance,a current supply conductor connected to said conductive coating andhaving a terminal for connection to an external circuit, and a separatesupply conductor connected to the conductive support for the cathode andhaving a terminal for connection to an external circuit, whereby apotential difference may be applied between the conductive support andthe conductive coating on the emissive material.

JOHAN LODEWIJK HENDRIK JONKER.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS

